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Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-querystd.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/vidioc-querystd.xml | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/DocBook/media/v4l/vidioc-querystd.xml b/Documentation/DocBook/media/v4l/vidioc-querystd.xml index 222348542182..3ceae35fab03 100644 --- a/Documentation/DocBook/media/v4l/vidioc-querystd.xml +++ b/Documentation/DocBook/media/v4l/vidioc-querystd.xml @@ -59,6 +59,16 @@ then the driver will return V4L2_STD_UNKNOWN. When detection is not possible or fails, the set must contain all standards supported by the current video input or output.</para> +<para>Please note that drivers shall <emphasis>not</emphasis> switch the video standard +automatically if a new video standard is detected. Instead, drivers should send the +<constant>V4L2_EVENT_SOURCE_CHANGE</constant> event (if they support this) and expect +that userspace will take action by calling <constant>VIDIOC_QUERYSTD</constant>. +The reason is that a new video standard can mean different buffer sizes as well, and you +cannot change buffer sizes on the fly. In general, applications that receive the +Source Change event will have to call <constant>VIDIOC_QUERYSTD</constant>, +and if the detected video standard is valid they will have to stop streaming, set the new +standard, allocate new buffers and start streaming again.</para> + </refsect1> <refsect1> |